There are many processes that involve the addition of chemical substances to fluids in which the amount of added material is to be adjusted according to physical and chemical criteria. Some of those processes will require a degree of treatment, either physical or chemical, which is determined by the state of the treatment apparatus. Examples can be found in hydroponic gardening, drug manufacture, maintenance of decorative pools, marine animal "farming, " and others.
Another, and a very important example, is found in the processing of the water in swimming pools. In addition to its recreational use, the water in swimming pools represents a very important energy storage medium in private and public energy conservation systems. Because of the large volume of water in a swimming pool, it is capable of absorbing, storing and releasing very large quantities of heat with relatively small temperature changes. That makes it specially useful as a place in which to store heat when cooling living spaces and as a source of heat when heating living spaces. And, the pool is an excellent place in which to store solar energy with or without an energy collection cover, as a solar energy collector.
On the other hand, to use a swimming pool as a heat storage element results in pool water temperatures that are higher at times than the temperatures that are maintained for recreational use alone. Algae, pathenogenic bacteria, and pool water chemistry control are likely to be a more difficult problem in the swimming pool that also serves as a thermal energy storage unit.
The problem of dirt and debris removal remains unchanged except that the usage of pool covers, which also enhance solar energy collection, results in the pool being covered for more of the time. This is offset by the fact that the pool water is subsequently warmer and recreational use is feasible for more months of each year. Economic and social factors dictate that most heat storage water pools will have an exposed solar surface and will utilize removable covers for additional recreational as well as heat storage use.
Both mechanical filtration and chemical management are required, and at the least, the chemical processing will need to be much more precisely controlled. Mechanical filtration must be controlled if the amount of energy expended on water circulation is to be minimized. The best criterion for filtration is the "turnover" frequency when all of the pool water is moved through the filter based upon the conditions of local environment. The "turnover" frequency having been selected, and the pool volume being known, the parameters are volumetric pumping rate and time. Because the size of pumps and filters is fixed at each installation, the practical variable is time.
On the chemical side, the major variables are pH and the need for a bacteriacide and algicide. In practice, some form of sanitizer, typically chlorine is used to control bacteria and algae. The effectiveness of the chlorine, the swimming quality of the water, and the corrosion rate is determined by controlling pH. In each geographic area, pH tends to change in one direction or the other requiring only addition of acid or base as required. In most cases it is acid that needs to be added. It is much preferred that these materials be added at a very slow rate over a long period except when chlorine "shocking" is required. With time, algae and bacteria mutants, resistant to the chlorine treatment, will survive and multiply in the pool. To kill the individuals of that strain, a massive dose of a different bacteriacide and algicide is applied to the pool. In most cases the "shocking" dose is formed by a chlorine component other than what is used for sanitizing maintenance control.
The measurement and control of pool water composition has been beyond the capability of most pool owners unless the process is reduced to simplified approximations. In most cases, control is accomplished as a function of time. Measurements and chemical additions are made daily, at best, and more often on the one or two days of the week that the pool maintenance person makes his rounds. Chemical additions are made in batches. The concentrations that result cause excessive corrosion, both in the pool and in the water circulation system. Breakdown of heating and filtration systems may go undetected for long periods. Because they operate only periodically, the fact that these units are not operating when the pool is being serviced may be interpreted as being normal.
This swimming pool example is only one of many in which combined physical and chemical control is exercised. It is, however, a very important example, not only because of the very large number of existing private swimming and spa pools, but because those pools represent an important existing facility that is easily applied to the problem of conserving energy and utilizing solar energy.
The availability of microprocessors has made it possible to solve very complex algorithms at far less cost than was possible with discrete digital and analog devices and the relays of prior times. The microprocessor has not always simplified the task of sensing conditions and taking corrective actions. Sometimes it leads to greater complications. This invention is related to those tasks, the tasks of sensing conditions and applying the controlling actions to be accomplished, in most cases, in conjunction with algorithm solution, whether by the new computers or the old discrete components.